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Seminar on Service Oriented Architecture

Join our seminar to learn about the principles of Service Oriented Architecture (SOA) and how it is implemented in Web Services. Explore important standards, communication patterns, service composition, SOAP, REST style, WS-Addressing, and more.

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Seminar on Service Oriented Architecture

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  1. Seminar on Service Oriented Architecture Web Services Chapter 19 of Coulouris SOA Seminar

  2. In A Nutshell From Globus.org (Grid computing) SOA Seminar

  3. With Stubs From Globus.org (Grid computing) SOA Seminar

  4. Some Important Standards SOA Seminar

  5. Some Important Standards Very important with respect to XML web services. SOA Seminar

  6. Web Services • Provide service interfaces. • Communicate using request and reply messages made of SOAP or some other XML document. • Have an Interface Definition Language (IDL) called WSDL (Web Service Definition Language) • May be looked up in a web service UDDI registry (Universal Directory and Discovery Service). • Are language independent. • May be synchronous or asynchronous. SOA Seminar

  7. Web Services Registry publish lookup Client Service Exchange xml SOA Seminar

  8. Web Services Infrastructure and Components Applications Security Directory service Orchestration Web Services Service descriptions (in WSDL) SOAP URIs (URLs or URNs) XML HTTP, SMTP or other transport SOA Seminar

  9. Communication Patterns • In general, web services use either a synchronous request- reply pattern of communication with their clients or they communicate by asynchronous messages. • The client does not block on asynchronous calls. Do you block when you are expecting an important phone call? If not then you are planning on handling the call asynchronously. • To allow for a variety of patterns, SOAP is based on the packaging of single one-way messages. • SOAP is used to hold RPC style parameters or entire documents. • SOAP may be used over different transports (SMTP, TCP, UDP, or HTTP) SOA Seminar

  10. Service References • URI’s are Uniform Resource Identifiers. • URL’s are Uniform Resource Locator URI’s that include location information. Thus, resources pointed to by URL’s are hard to move. • URN’s are Uniform Resource Name URI’s that include no location information. • A URN lookup service may be used to determine a URL from a URN. • URL’s are the most frequently used form of URI. Examples (the third is from Wikipedia): 1. URL: http://www.cmu.edu/service 2. URN: urn:ISBN:0-111-2345-6 3. "you can find urn:ietf:rfc:3187 (URN) over at http://tools.ietf.org/html/rfc3187.html (URL)." SOA Seminar

  11. Web Service Composition flight booking a flight booking b Travel Agent Client Service hire car booking a hire car booking hotel booking hotel booking b a b What concerns are not shown? Transactions, Security (privacy, identification, authentication, authorization), Reliability, Orchestration tooling, Interoperability through Standards, RPC or Messaging, Service Level agreements SOA Seminar

  12. SOAP • Defines a scheme for using XML to represent the contents • of request and reply messages as well as a scheme for • the communication of XML documents. • It is intended that a SOAP message can be passed via • intermediaries on the way to the computer that manages • the resources to be accessed. • The intermediaries may process the SOAP to provide security or transaction support as well as other services. • Typically, the SOAP header is processed by intermediaries and the SOAP body holds the request or reply. SOA Seminar

  13. SOAP Envelope envelope header header element header element body body element body element SOA Seminar

  14. Request Without Headers env:envelope xmlns:env =namespace URI for SOAP envelopes env:body m:exchange xmlns:m = namespace URI of the service description m:arg1 m:arg2 Hello World Why is envelope in a different namespace than arg1? Consider GreenBayPackers:MikeMcCarthy and CMU:MikeMcCarthy SOA Seminar

  15. Corresponding Reply xmlns:env = namespace URI for SOAP envelope env:envelope env:body m:exchangeResponse xmlns:m = namespace URI for the service description m:res1 m:res2 World Hello SOA Seminar

  16. HTTP POST Example POST /examples/stringer endpoint address HTTP header Host: www.cdk4.net Content-Type: application/soap+xml action Action: http://www.cdk4.net/examples/stringer#exchange <env:envelope xmlns:env= namespace URI for SOAP envelope > <env:header> </env:header> Soap message <env:body> </env:body> </env:Envelope> A transport protocol is required to send a SOAP document to its destination. Other transports may be used. WS-Addressing may be used to include destination and source. Thus, different protocols might be used over different parts of the route of a message. SOA Seminar

  17. REST Style WS POST /examples/stringer Use a URI and an HTTP method to select what needs to be done. Host: www.cdk4.net Drop the SOAP and use name value pairs for the request. Use XML or JSON for the response. Appropriate for ad-hoc mashups. Some believe that REST is not appropriate for enterprise computing. SOA Seminar

  18. WS-Addressing <S:Envelope xmlns:S="http://www.w3.org/2003/05/soap-envelope" xmlns:wsa="http://schemas.xmlsoap.org/ws/2004/08/addressing"> <S:Header> <wsa:MessageID> uuid:6B29FC40-CA47-1067-B31D-00DD010662DA </wsa:MessageID> <wsa:ReplyTo> <wsa:Address>http://business456.example/client1</wsa:Address> </wsa:ReplyTo> <wsa:To>http://fabrikam123.example/Purchasing</wsa:To> <wsa:Action>http://fabrikam123.example/SubmitPO</wsa:Action> </S:Header> <S:Body> ... </S:Body> </S:Envelope> Address information included within the document rather than only being specified by the transport. What does this buy us? SOA Seminar

  19. Distributed Objects? At first glance, the interaction between client and server seems like RMI. We will look at RMI soon. But, RMI permits the creation of remote objects. These may then be accessed via remote references. Web services may create and use objects but never return a remote reference to a remote object. A web service is a single object that offers a set of procedures. Web services are simpler than distributed objects. Simple is good. SOA Seminar

  20. Service Descriptions • The primary means of describing a web service is by using • WSDL (the Web Services Description Language) • XML Schema may be used to describe documents. • WSDL makes use of XML Schema to describe an exchange of • messages. • A Service Description (WSDL document) is an IDL (interface • definition language) plus it contains • information on how and where the service may be accessed. • It contains an abstract part and a concrete part. The abstract • part is most like a traditional interface. The concrete part tells • us how and where to access the service. SOA Seminar

  21. The Main Elements in a WSDL Description definitions services interface bindings types message target namespace document style request-reply style how where concrete abstract A binding is a choice of protocols. A service holds an endpoint address. Client or server side code may be generated automatically from the WSDL. A WSDL document may be accessed directly or indirectly through a registry like UDDI (Universal Directory and Discovery Service). SOA Seminar

  22. WSDL MEPS Name Messages sent by Client Server Fault message Request Reply In-Out may replace Reply Request no fault message In-Only Request Robust In-Only may be sent Reply Request Out-In may replace Reply Request no fault message Out-Only Request may send fault Robust Out-Only Which of these does a fire alarm service provide? SOA Seminar

  23. XSDL and WSDL • XSDL (The XML Schema Definition Language) allows us to describe the structure of an XML message • WSDL allows us to describe message exchanges Notes from article by Aaron Skonnard. See the schedule for the URL of this article SOA Seminar

  24. WSDL • A message exchange is called an operation. • Related operations are grouped into interfaces. • A binding specifies concrete details about what goes on the wire. SOA Seminar

  25. WSDL • Describes the contract between applications. • Can be automatically generated from a collection of Java or C# classes. • Can be read by utilities that generate client side proxy code or server side skeletons. • See wsimport (JDK 6.0) or wsdl.exe on the Microsoft side. In Netbeans just drag and drop a web reference. SOA Seminar

  26. WSDL Structure <definition> <!– abstract definitions  <types> <messages> <portType> <!– concrete definitions  <binding> <service> </definition> SOA Seminar

  27. WSDL Structure <definition> <!– Terms found in application code  <types> <messages> <portType> <!– Handled by XML infrastructure  <binding> <service> </definition> SOA Seminar

  28. WSDL Structure <definition> <types> - a container for XSDL Type definitions - element names may be defined here as well SOA Seminar

  29. WSDL Structure <definition> <types> For example, in Google’s WSDL, GoogleSearchResult is defined as a complex type with many elements. SOA Seminar

  30. WSDL Structure <definition> <types> <message> - May have more than one part (think parameters) - Define the input or output of an operation - RPC style messages associate a name with a type (defined above) - Document style messages associate a name with an XML element </definition> SOA Seminar

  31. WSDL Structure <definition> <types> <message> Two examples: - In Google’s WSDL, a doGoogleSearch message is defined with many parts of basic xsd types. - In Google’s WSDL, a doGoogleSearchResponse message is defined as of type GoogleSearchResult </definition> SOA Seminar

  32. WSDL Structure <definition> <types> <messages> <portType> - The definition of an interface or group of operations - The term “portType” will be replaced with the term “interface” in WSDL 1.2 - Each operation has a name and normally specifies both input and output messages </definition> SOA Seminar

  33. WSDL Structure <definition> <types> <messages> <portType> - For example, in Google’s WSDL, GoogleSearchPort contains three operations. - The operation doGoogleSearch has an input message (doGoogleSearch) and an output message (doGoogleSearchResponse.) </definition> SOA Seminar

  34. WSDL Structure <definition> <types> <messages> <portType> <binding> - Each binding has a unique name that is associated with a particular interface. - The protocol used is specified. - Details found here specify how the data will look on the wire. </definition> SOA Seminar

  35. WSDL Structure <definition> <types> <messages> <portType> <binding> - For example, in Google’s WSDL, the binding name GoogleSearchBinding is introduced and is associated with the interface GoogleSearchPort. - Each operation within that interface is described as soap operations. </definition> SOA Seminar

  36. WSDL Structure <definition> <types><messages><portType> <binding> <service> - Defines a collection of ports (endpoints) that exposes a particular binding - An address is associated with a binding </definition> SOA Seminar

  37. WSDL Structure <definition> <types><messages><portType><binding> <service> For example, in Google’s WSDL, the service name GoogleSearchService is introduced. The interface GoogleSearchPort is associated with the binding GoogleSearchBinding. The service element holds the address of the service. </definition> SOA Seminar

  38. Writing A Google Client • Get the WSDL from http://www.google.com/apis/ • If using .NET run wsdl.exe on GoogleSearch.wsdl. • If using Java and Axis run wsdl2java.bat on GoogleSearch.wsdl. • wsdl2java.bat holds the line java org.apache.axis.wsdl.WSDL2Java %1 The WSDL2Java class is in axis.jar SOA Seminar

  39. A Google Client in Java // Running a simple Google RPC client for spell checking import GoogleSearch.*; // wsdl2java generated package public class MyGoogleClient{ private static String endpointAddress = "http://api.google.com/search/beta2"; public static void main(String[] args) throws Exception { if(args.length != 1) { System.out.println("Usage1: java MyGoogleClient wordToSpellCheck"); System.out.println( "Usage2: java MyGoogleClient \"a phrase to spell check\""); System.exit(0); } SOA Seminar

  40. System.out.println("Contacting Google Web Service at " + endpointAddress); System.out.println("Checking on spelling of '" + args[0]+"'"); GoogleSearchServiceLocator loc = new GoogleSearchServiceLocator(); GoogleSearchPort gp = loc.getGoogleSearchPort(); String answer = gp.doSpellingSuggestion( "n6lHU/FQFHIHzpbzRTPFvrUP4Cw+/k+N", args[0]); if(answer == null) System.out.println("Google likes the spelling of '" + args[0]+"'" ); else System.out.println("Google suggests the spelling '" + answer +"'" ); } } SOA Seminar

  41. GoogleSpring2005\java>java MyGoogleClient "Cornegi Melon Universeti" Contacting Google Web Service at http://api.google.com/search/beta2 Checking on spelling of 'Cornegi Melon Universeti‘ Google suggests the spelling 'Carnegie Mellon University' SOA Seminar

  42. A Google Client in C# // run a client against Google's web service using System; namespace ConsoleApp { class GoogleClient { public static void Main(string[] args) { try { GoogleSearchService s = new GoogleSearchService(); SOA Seminar

  43. Console.WriteLine("Enter word to spell check"); String word = Console.ReadLine(); String answer = s.doSpellingSuggestion( "n6lHU/FQFHIHzpbzRTPFvrUP4Cw+/k+N", word); Console.WriteLine("Google returned " + answer); } catch(Exception ) {Console.WriteLine("Google threw an exception");} } } } SOA Seminar

  44. UDDI • An acronym for Universal Directory and Discovery Services. • A directory service for use with web services. • One way to obtain service descriptions. • May be used within organizations to perform lookups for WSDL documents. • Supports white pages (lookup by name) and yellow pages (lookup by attribute) • Provides a publish/subscribe interface. • Uses replication among many servers for scalability. • JAXR (The Java API for XML Registries) may be used to interact with UDDI. UDDI has not been as widely supported as was originally hoped. SOA Seminar

  45. UDDI Data Structures businessEntity businessServices human readable businessServices information businessServices bindingTemplate about the publisher human readable bindingTemplate information URL bindingTemplate tModel about a information family of services tModel about the URL service interfaces service interfaces tModel key URL service descriptions key key SOA Seminar

  46. Web Services Security Stack (Quick Overview) XML Web Services Security SAML (Security Assertion ML),XKMS (XML Key Management Specification), XACML (eXtensible Access Control Markup Language) XMLDSIG (W3C) XMLENC (W3C) .NET Crypto API’s Java Security API’s We will dive deeper when we cover cryptography. SOA Seminar

  47. Travel Agent Scenario • 1. The client asks the travel agent service for information about a set of services; for example, flights, car hire and hotel bookings. • 2. The travel agent service collects prices and availability information and sends it to the client, which chooses one of the following on behalf of the user: • (a) refine the query, possibly involving more providers to get more information, then repeat step 2; • (b) make reservations; • (c) quit. • 3. The client requests a reservation and the travel agent service checks availability. • 4. Either all are available; • or for services that are not available; • either alternatives are offered to the client who goes back to step 3; • or the client goes back to step 1. • 5. Take deposit. • 6. Give the client a reservation number as a confirmation. • 7. During the period until the final payment, the client may modify or cancel reservations The Business Process Execution Language (BPEL) is used to write such scenarios in XML. Many BPEL designer tools are based on BPMN. BPEL XML is the standard result. SOA Seminar

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